The present invention generally relates to a generalized extracorporeal support system and method to oxygenate or hyper-oxygenate blood. More specifically, the present invention relates to a generalized extracorporeal support system and method to oxygenate blood from a patient by withdrawing the blood and mixing the blood with an oxygen supersaturated solution for localized or systemic infusion back to the patient.
When a patient suffers from acute or transient ischemia, oxygenation and delivery of blood to ischemic and postischemic tissue and/or organ sites is desired in order to prevent or minimize damage to the tissue and/or organ sites. For example, when a patient suffers from an acute myocardial infarction or a heart attack, support of the myocardium during or immediately following the infarction is desired. During a heart attack, the coronary arteries fail to provide adequate blood flow to the heart muscle. If the lack of a supply of oxygenated blood to the heart muscle continues for a prolonged period of time, irreversible damage to the heart can result.
In addition, many patients suffer reperfusion injury, i.e. slow coronary reflow or xe2x80x9cno reflowxe2x80x9d, following successful angioplasty of occlusions responsible for an acute myocardial infarction or myocardial ischemia. To prevent or minimize reperfusion injury, hyperoxemic blood may be actively perfused into the coronary artery to improve blood flow with increased intracoronary pressure. In addition, the high level of oxygenation in the blood should improve oxygen delivery when diffusional distances between capillaries with normal blood flow are large. Finally, the compensatory hypercontractility of the normally perfused left ventricular segments may also benefit from an increase in oxygen supply.
Furthermore, during percutaneous transluminal coronary angioplasty (PTCA), the balloon inflation time is limited by the patient""s tolerance to ischemia caused by the balloon inflation. Certain patients are especially at risk of ischemia because of the location or type of lesion, the amount of myocardium at risk, or poor left ventricular function, thereby limiting the performance of effective PTCA. Thus, active perfusion of hyperoxemic blood during PTCA is desired to lessen ischemia and to protect and support the myocardium during balloon inflation and to prolong the tolerated inflation time. Active perfusion of hyperoxemic blood after PTCA may also be desired to accelerate reversal of ischemia and/or recovery of myocardial function.
Conventional membrane or microporous hollow fiber oxygenators have been utilized to oxygenate blood in extracorporeal circuits. In these devices blood is withdrawn from a patient and by circulating the blood through the conventional oxygenator, the blood is oxygenated and delivered back to the patient.
Several disadvantages are associated with use of a conventional oxygenator to directly oxygenate blood. For example, the oxygenator requires a significant priming volume of blood, i.e. the volume of extracorporeal blood within the oxygenator for preparation of oxygen enriched blood. Because more than one quart of priming volume of extracorporeal blood is needed for an adult patient when using the conventional membrane oxygenator, a heat exchanger is usually necessary to maintain the temperature of the blood and a blood transfusion is also frequently necessary. Moreover, due to the large blood membrane oxygenator surface contact area and a relatively slow blood flow rate within the oxygenator, inflammatory cell reactions may be provoked and, in addition, a relatively aggressive anticoagulation therapy such as systemic heparinization may be necessary. Due to the large priming volume of the oxygenator, the oxygenator cannot be easily turned on and off because of the difficulties in flushing the blood from the system with saline and, upon cessation of flow, stagnant blood would result in thrombus formation. Additionally, the large priming volume increases the amount of blood at risk of thrombi formation, especially when stopping and starting the oxygenation. Furthermore, the use of conventional oxygenators to oxygenate blood involves high costs associated with the replacement of the oxygenator for each use. Finally, the maximum partial pressure of oxygen that can be achieved in blood with a conventional oxygenator is 1 bar. As a result of the challenges in using the conventional oxygenators, treatment of regional organ ischemia with conventional oxygenators has not been developed clinically.
With direct intravascular infusion of an oxygen supersaturated physiologic infusate into the blood stream, optimal mixing of the infusate with the blood may be difficult to obtain. For example, inadequate mixing of the infusate with blood may result in dangerous microbubble formation, and direct intravascular infusion would thus require the use of sensors to monitor the intravascular oxygen levels and to detect the intravascular presence of microbubbles.
Accordingly, there remains a need in the art for a safe, simple, efficient and cost-effective system and method for oxygenating a patient""s blood by withdrawing and mixing the blood with an oxygen supersaturated physiologic infusate which provides for near physiologic flow rates within the system and which does not require a high priming volume of blood, a heat exchanger or aggressive systemic anticoagulation therapy.
There remains a further need in the art for a system and method for mixing and infusing a patient""s blood and oxygen supersaturated physiologic infusate to a tissue or organ site of interest which provides adequate mixing of the infusate with the blood and which provides oxygenation of the blood at a target level.
There remains yet a further need in the art for a system and method for producing and delivering oxygen-supersaturated blood to a tissue or organ site of interest without bubble nucleation or growth during mixing of the infusate with the blood or during infusion in the blood stream.
The present invention meets the foregoing needs by providing a system and method of treating blood from a patient extracorporeally by mixing the blood with an oxygen supersaturated infusate to generate hyperoxemic blood to be infused back to the patient.
The system of the present invention preferably utilizes aqueous oxygen as the oxygen supersaturated infusate to generate normoxemic or hyperoxemic blood. Aqueous oxygen is a highly concentrated form of oxygen-supersaturated solution that is a liquid phase combination of an aqueous carrier and oxygen, where the volume of dissolved oxygen, normalized to standard temperature and pressure, ranges from approximately 0.5 up to 3 times the volume of the aqueous carrier. Because of the high concentration of oxygen in aqueous oxygen, a relatively small volume of aqueous oxygen can be infused into the blood for alleviation or correction of hypoxemia or production of hyperoxemia. Therefore, the use of aqueous oxygen as the oxygen supersaturated infusate minimizes the volume of the aqueous carrier added to the blood stream.
The system of the present invention provides an extracorporeal tubing, through which blood from a patient is circulated, a blood pump for withdrawing blood from and delivering blood to the patient, an aqueous oxygen generator or pump with output tubes and a chamber for connecting the extracorporeal tubing and the aqueous oxygen output tubes and providing the necessary mixing function. The system may also include sensors for monitoring certain parameters of the blood, access ports for intermittent analysis of the blood, hydraulic components to manage the hydrodynamics of the blood flow, bubble traps and bubble detectors to ensure bubble-free delivery of the oxygenated blood, system shunts or system shutdown devices to manage system related failures and a hemofilter for filtering the aqueous carrier from the hyperoxemic blood prior to infusion of the blood to the patient.
The system and method of the present invention obviates the need for a heat exchanger and for an aggressive, systemic anticoagulation therapy due to the small blood priming volume and the near physiologic blood flow rates through the system. Furthermore, the system and method of the present invention provides adequate mixing and infusion of the aqueous oxygen infusate and the blood without bubble nucleation or growth. The aqueous oxygen infusate can yield a blood pO2 of greater than 1000 mm Hg so as to provide support and expedite the treatment of ischemia with hyperoxemic blood perfusion.
The system and method of the present invention provides for simple blood withdrawal and delivery access via devices already in place in the patient for interventions, such as the side-arm of a sheath and a coronary guide catheter for intracoronary infusion. In addition, easy access to the blood in the extracorporeal system allows for utilization of devices to monitor parameters of the blood in the system and to vary system operations accordingly.